Semiconductor devices such as BGA and LGA packages are subjected to a burn-in test prior to shipment, which applies stresses due to a high temperature to the semiconductor device. This eliminates devices in advance in which failures would occur in a certain period after shipping. Sockets used for the burn-in test generally are in two types. One is an open-top type socket whose cover member is vertically reciprocated. The other is a clamshell type socket whose cover member is rotated. For an open-top type socket, JP published application No. 2009-140629, U.S. Publication No. 2010-0248518 A1 (patent document 1) which is incorporated herein by reference, for example, discloses a socket that enables mounting and removing precisely an electronic device including surface mounted semiconductor devices such as BGA and Chip Scale Package (CSP) devices.